Sebastian Stepanow

Affiliation: ETH Zurich

Date: December 9, 2020; 17:00 – 18:00

Single-atom electron paramagnetic resonance in a scanning tunneling microscope

Scanning tunneling microscopy (STM) is a unique technique to achieve subatomic spatial resolution with simultaneous local spectroscopic information. The demonstration of spin sensitivity in STM experiments enabled the study of single magnetic atoms on a surface and their interactions. Despite these great advances, the energy resolution remains limited in tunneling-spectroscopy modes by the thermal energy broadening of the electronic tip and sample states (>1 meV at 4 K). This broadening limits the precise sensing of low-energy excitations, e.g., spin-flip excitations, which motivated efforts to reduce the STM operational temperature to the mK range and to apply large magnetic fields to obtain the required sensitivity.

Another promising way to overcome the thermally-limited energy resolution is to employ a resonance technique. In this regard, electron paramagnetic resonance (EPR) is an established method that has found diverse applications such as the identification of free radicals in chemical reactions, detection of spin-labeled molecules in biological systems, or the study of molecular nanomagnets.
Recently, the two techniques were combined to probe magnetic interactions and properties of single atoms on surfaces [1]. In this presentation, I will introduce the EPR-STM technique and highlight recent advances. Moreover, I will address the coupling of microwave driving fields into the STM junction [2] and discuss our current understanding of the underlying mechanism in EPR-STM [3].

[1] Baumann et al., Science 350, 417 (2015).
[2] Seifert et al., Physical Review Research 2, 013032 (2020).
[3] Seifert et al., Science Advances 6, eabc5511 (2020).